The invention relates to a radar apparatus, provided with an antenna, a transmitting unit, a receiving unit and a detection unit which, for objects incorporating fast moving parts, such as helicopters, determines the positions of these objects on the basis of successive measurements, whereby the measuring values, via a first range-azimuth memory, are applied in groups to the detection unit which, per group, can generate a detection, which detections are applied to a second range-azimuth memory; further provided with a clusterer which determines the positions of individual detections or clusters of detections in the second range-azimuth memory and delivers these positions for further processing.
A radar apparatus of this kind is known from U.S. Pat. No. 4,389,647. In the above-mentioned radar apparatus, the radar parameters, like pulse repetition frequency and antenna rotation speed, have been selected such that the blade flashes become visible. These blade flashes are strong radar echoes which are produced at the moment that the rotor blades are perpendicular to the radar beam, making good radar reflectors.
For a conventional surveillance radar, the radar parameters are selected on entirely different grounds. So it logically follows that such a surveillance radar does not, or only insufficiently, detect the above blade flashes, which precludes these blade flashes from being made the basis for a detection principle. The detection probability is small.
The invention has for its object to provide a solution to this problem. The invention is based on the observation that when the strength of a target reflection is measured with a number of radar pulses and the standard deviation is determined on the basis of the resulting measuring values, theis standard deviation is unexpectedly large when the target is a helicopter.
This is also the case, if the measurements are performed with a conventional search radar. Special provisions, however, will have to be made to compensate for the effect of the antenna rotation.
The invention is a radar apparatus provided with a detection unit, which operates on the basis of the above-mentioned observation.
The invention is particularly suitable to be used as a search radar, but it can also be used advantageously in other radar applications, whereby the radar beam dwells on the target only for a brief period.